Debt Instrument, Covenant Compliance, Limit Of Securing Indebtedness

No definition available.

Name:	swn_DebtInstrumentCovenantComplianceLimitOfSecuringIndebtedness
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument, Covenant Compliance, Limit Of Securing Indebtedness, Percent Of Consolidated Net Tangible Assets

+ References

No definition available.

+ Details

Name:	swn_DebtInstrumentCovenantComplianceLimitOfSecuringIndebtednessPercentOfConsolidatedNetTangibleAssets
Namespace Prefix:	swn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Total debt divided by EBITDAX.

+ References

No definition available.

+ Details

Name:	swn_LeverageRatio
Namespace Prefix:	swn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Leverage Ratio, Amount of Credit Limit

+ References

No definition available.

+ Details

Name:	swn_LeverageRatioAmountOfCreditLimit
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Leverage Ratio, Percentage of Credit Limit

+ References

No definition available.

+ Details

Name:	swn_LeverageRatioPercentageOfCreditLimit
Namespace Prefix:	swn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Limit of Unrestricted Cash and Cash Equivalents

+ References

No definition available.

+ Details

Name:	swn_LimitOfUnrestrictedCashAndCashEquivalents
Namespace Prefix:	swn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Minimum Current Ratio

+ References

No definition available.

+ Details

Name:	swn_MinimumCurrentRatio
Namespace Prefix:	swn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of subsidiary's or equity method investee's stock owned by parent immediately after all stock transactions.

+ References

No definition available.

+ Details

Name:	us-gaap_SubsidiaryOrEquityMethodInvesteeCumulativePercentageOwnershipAfterAllTransactions
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_CreditFacilityAxis=swn_October2020AmendmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_LineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=swn_A2018RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	swn_DebtInstrumentCovenantCompliancePeriodOfComplianceAxis=swn_OnOrAfterJune302020Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_EurodollarMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_BaseRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Debt (2018 Revolving Credit Facility - Narrative) (Details)	1 Months Ended		3 Months Ended	12 Months Ended
	Oct. 31, 2020 USD ($)	Apr. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Subsidiary ownership				100.00%
Letters of credit outstanding				$ 233,000,000
Debt instrument				3,171,000,000	$ 2,262,000,000
October 2020 Amendment
Debt Instrument [Line Items]
Basis points	25.00%
Limit of unrestricted cash and cash equivalents	$ 200,000,000
Line of Credit \| 2018 Revolving Credit Facility \| Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 3,500,000,000
Current borrowing capacity	$ 2,000,000,000.0	2,000,000,000.0
Debt instrument limit of securing indebtedness		$ 2,000,000,000.0
Debt instrument limit of securing indebtedness, percent of consolidated net tangible assets		25.00%
Minimum current ratio			1.00
Leverage ratio, percentage of credit limit			10.00%
Leverage ratio, amount of credit limit			$ 150,000,000
Debt instrument				$ 700,000,000
Line of Credit \| 2018 Revolving Credit Facility \| Revolving Credit Facility \| On Or After June 30, 2020
Debt Instrument [Line Items]
Leverage ratio			4.00
Line of Credit \| 2018 Revolving Credit Facility \| Revolving Credit Facility \| Eurodollar \| Minimum
Debt Instrument [Line Items]
Basis points		1.75%
Line of Credit \| 2018 Revolving Credit Facility \| Revolving Credit Facility \| Eurodollar \| Maximum
Debt Instrument [Line Items]
Basis points		2.75%
Line of Credit \| 2018 Revolving Credit Facility \| Revolving Credit Facility \| Base Rate \| Minimum
Debt Instrument [Line Items]
Basis points		0.75%
Line of Credit \| 2018 Revolving Credit Facility \| Revolving Credit Facility \| Base Rate \| Maximum
Debt Instrument [Line Items]
Basis points		1.75%